Effects of Metarhizium humberi conidia formulated with micronized carnauba wax on self-grooming behaviours by Aedes aegypti adults.

Aedes aegypti L. (Diptera, Culicidae), the key vector of viral diseases to humans in the tropics, is susceptible to infection by entomopathogenic fungi. Self-grooming behaviour, which remains largely unstudied for mosquitoes, may possibly interfere with fungal infection through the cuticle. In this study, self-grooming by A. aegypti adults exposed to Metarhizium humberi Luz, Rocha & Delalibera 2019 (Hypocreales, Clavicipitaceae) conidia supplemented or not with micronized carnauba wax (MCW) led to a decrease of non-germinated conidia and of early germinative stages from their body surface up to 24 h after exposure to a fungus-treated surface. Self-grooming behaviours by adults distinctly showed increased low-level, spontaneous and stimulus-independent self-grooming after exposure to conidia with or without added MCW or only to MCW. The first pair of legs simultaneously scraped the proboscis, antennae and wings; in three separate actions, the third pair of legs scraped (a) each other, (b) the first and second legs and (c) the gonapophyses. Immediately after exposure, conidia, a conidial/MCW mixture or MCW (without fungus) was readily detectable on tarsi, tibias and femurs (especially of the first and second leg pairs), gonapophyses, proboscis, antennae and wings. In mobile adults, mean conidial numbers dropped approximately fivefold during the 24 h immediately after exposure, but especially during the first 6 h, regardless of the conidial preparation and then, to a lesser extent, in the remaining 18 h. For cold-immobilized adults, during the first day post-exposure, conidial losses were distinctly lower or insignificant. MCW neither increased the number nor enhanced the retention time of conidia on the cuticle during the time tested. These findings strengthen the importance of considering self-grooming of mosquitoes - particularly regarding A. aegypti, the vector examined here - when developing specific fungal formulations for use in biological control.